Time Division Duplex (TDD) is flexible in terms of possibility to adapt time resources between uplink and downlink transmissions, i.e. between number of uplink and downlink subframes. By dynamically changing a ratio between the number of subframes for uplink and downlink, respectively, such as to match the instantaneous traffic situation, performance experienced by an end-user may be improved. The ratio between uplink/downlink subframes is determined by an uplink/downlink (UL/DL) configuration, referred to as TDD configuration hereinafter, of a radio base station.
Another benefit of dynamic TDD is network energy savings, i.e. an improvement of downlink resource utilization allows a radio base station, such as an evolved Node B (eNB), to configure DL subframes more efficiently so that energy savings may be achieved.
A heterogeneous network may typically comprise macro nodes and micro nodes. The macro nodes have a higher transmit power than the micro nodes. In general, it is not preferable to change the TDD configuration for the macro nodes, at least not on a small time scale. However, for heterogeneous networks, it may be that only a few user equipments (UEs) are active simultaneously per micro node, which implies a high possibility that many neighbouring nodes, or cells, are momentarily empty. The traffic dynamics are expected to be large with relatively low average load, but high instantaneous data rates. It this case, the traffic asymmetry between uplink and downlink directions may become a significant. Therefore, dynamic TDD configuration becomes attractive.
When the neighbouring nodes are configured with different TDD configurations, interference between UL and DL including both eNB-to-eNB (DL-to-UL) and UE-to-UE (UL-to-DL) interference needs to be considered. The cross-link interference should be either mitigated or avoided so that the benefit of dynamic TDD could be achieved.
In scenarios of dynamic uplink and downlink (UL/DL) allocation in a TDD cellular system, different neighbouring eNBs will use different TDD configurations from time to time. As an example, a certain cell could become an ‘aggressor cell’, which uses a configuration different from a neighbouring ‘victim cell’. For instance, in a specific subframe, there is a DL subframe of the aggressor cell, while in the same specific subframe, there is a UL subframe for the victim cell. Hence, in the specific subframe, the uplink of victim cell will be interfered by eNB-to-eNB interference from the aggressor cell. A problem is, hence, how to measure and estimate the eNB-to-eNB interference.